In automated bulk material handling systems, it is necessary to store products for subsequent conveyance to succeeding stages of the process. In order to efficiently operate such systems, it is necessary to have an accurate measurement of the material in storage at any particular time.
Measurements of the level or load of bulk material in a silo of conventional design has presented many problems to the designer of the automated silo filling systems. These measurements are usually accomplished by inference. For example, the instantaneous level of a silo is considered to be a function of the length of time during which the silo is emptied at a presumed constant rate of discharge. In order to assure than an overload condition does not occur, large error margins must be considered thereby reducing the efficiency of the filling process.
Another method of measuring silo level is to use an ultrasonic probe, and electronic detector apparatus which measures the time differential between transmission and reception of an ultrasonic burst, which can readily be converted into a silo level figure.
Since bulk materials do not flow in a uniform manner, problems exist which create large error factors in the systems mentioned above. Rat holing and bridging are two effects caused by uneven flow characteristics of the bulk materials causing uneven distribution of the stored material. Large voids caused by uneven flow within the silo can provide a rather erroneous picture as to the actual level or volume of material actually stored.
Yet another method of measuring the load in a silo involves the use of load cells, wherein the entire silo is carried by support members having a load cell at each support. The cells provide a weight signal output which is directly related to the level of the silo. There are difficulties associated with this scheme because of the effects of electrical noice as explained below. Further, since the entire silo plus contents must be supported by the cells, lateral forces on the silo and transient noise caused thereby diminish the accuracy of the measurement.
The system of the present invention is designed to obviate many of the effects encountered in the prior art in respect to the measurement of levels of bulk material as shall be pointed out in the following description.